As indicated in FIGS. 1-2, a prior art fish processing machine has a main conveyor 18 with sets of flight pins 20-21 at regular intervals for conveying fish from a loading station 22 to a discharge station 23 while they are being processed. A fish hold-down conveyor 24 travels over the main conveyor through part of its travel to keep the fish from shifting position while they are being deheaded by a guillotine blade 25 and then have their throat tissue cut by a rotary tool 26. The blade 25 and the throat cutting tool 26 are both rigidly mounted on the frame of the machine, and the lower run of the hold-down conveyor 24 is engaged by four spring-loaded hold-down rollers 27-30 swing mounted to the machine frame.
A pin chain 31 is mounted alongside part of the length of the main conveyor 20 and presents a series of rigidly mounted head-positioning pins 32 on a conveyor chain to engage the fish behind the gills in its gill opening when they are positioned crosswise to the main conveyor 18 with their heads projecting over the pin chain. The main conveyor 18, hold-down conveyor 24 and pin chain 31 are driven by a sprocket and chain drive at the same speed by a motor 34 having a variable speed drive for discontinuous operation so that the fish can be stationary while being processed by the guillotine blade and throat cutting tool.
The discontinuous motion of the described prior art machine makes operation on fish of varying sizes difficult due to the disturbance caused to the position of the fish by stopping and starting the conveyor. Small fish, which by the nature of the mechanism are less securely held than large fish, are apt to be disturbed more than the large ones. The result is an unacceptable variance between the head cuts of large and small fish. Because the head positioning pins 32 mounted on the pin chain 31 change orientation as they start around the head sprocket for the pin chain, they tend to push the head of a conveyed fish forwardly relative to the main conveyor as that fish advances beyond the pin chain. Because a small fish has less room in its gill opening to accommodate this relative motion, a small fish is affected more than a large one. The result further contributes to an unacceptable variance between the head cuts of large and small fish.